1. Field of the Invention
The present invention relates to (1) a fire resistant composition, (2) a panel made thereof for forming external walls of various buildings and wherein the panel incudes those to form stud walls in wooden houses, and (3) a structure of an external wall, wherein the subject composition is designed to line or coat various structural elements made of metals, resins and/or lumber to be incorporated in steel-framed buildings, or to line the sizing parts or pieces used in ceramics industries or cement factories.
2. Prior Art
Fire resistance of construction parts such as steel beams for steel-framed buildings is prescribed in detail in the Japanese Building Standards Act, Enforcement Ordinance thereof, Article 107. The standards are given in the term of `fire resisting time` for each construction element such as walls, floors and pillars. The test method of judging fire resistance is set forth in `JIS A-1304` (Japanese Industrial Standards) recited in the Administrative Order No. 2999 issued in 1969 by the Ministry of Construction. JIS A-1304 is entitled: `Method of Testing the Fire Resistance of Construction Parts`, with the Order being entitled: `Implementation of Fire-Resistant Structures`. The test method of JIS A-1304 consists of (i) the heating of unloaded specimens, (ii) the heating of loaded specimens and (iii) the applying of impact to the specimens. The first item (i) above is further subdivided into: resistance to heat for duration of 30 min; ditto. for duration of 1 hour; ditto. for duration of 2 hours; and ditto. for duration of 3 hours. Specimens each coated with a fire-resistant lining should not be heated to an average temperature of 350.degree. C. within the prescribed period of 30 min or else, when kept in an oven whose temperature is about 1000.degree. C.
Many proposals have been made in an effort to meet the official requirements as to fire resistance, some of them being classified as the wet type, and others being the dry type. Japanese Patent Publication No. Hei.2-28555 discloses a fire-resistant composition, whose ingredients are a hydraulic cement, aluminum hydroxide and a certain carbonate. When heated, aluminum hydroxide will be dehydrated and the carbonate decomposed, both absorbing heat and respectively generating water vapor and carbon dioxide gas useful to extinguish the fire.
An enhanced fire resistance will reduce more or less the thickness of a fire resisting layer covering the construction elements or parts. In other words, the fire resisting layer must not only be improved in fire resistance but also be as thin as possible. Such a thin fire resisting layer will be beneficial in lowering the weight of construction parts and in expediting the construction of such parts. It is however noted that the proposals, such as recited above, have not realized yet a satisfactory fire resistant composition.
Not only the steel-framed buildings but also wooden houses or buildings must be more resistant to fire.
External walls including stud walls in wooden houses sometimes include outer panels that are covered with a fire resistant lining composed of a polystyrol foam and a cement. Those linings are bonded to plywood plates to form the so-called `lath-cut` panels, which are to be nailed or otherwise secured to supporting members. Mortar or plaster will be applied to the outer face of these lath-cut panels.
Similarly to the steel-framed buildings, the external walls of wooden houses must be approved as to their fire resistance in accordance with Japanese Building Standards Act. These walls have to comply with the standard of `secondary heating` as defined in the item `Measurement of Fire Resistance of Non-Combustible Construction Parts` in JIS A-1302. In this test of second class heating, the temperature of one major side face of the external wall should not rise above 260.degree. C. within a prescribed time, when placed in an atmosphere having a temperature of 1000.degree. C.
As mentioned above, the conventional fire-resistant lining on the external wall panels is usually composed of polystyrol foam and cement. Fire resistance of this lining is however not high enough to render its thickness less than 12 mm. Therefore, the plywood base plate carrying the lining about 12 mm thick must be about 9 mm thick. Mortar about 8 mm thick must be applied to the lining surface when the buildings or houses are constructed. Due to such a thick and heavy external wall, construction cannot be done easily within a short period and at a reasonable cost, further reducing an internal space adjacent to the wall. Highly and specially skilled workers must attend to the application of mortar, thus adding to the disadvantages noted above.
In cold districts, comfortable wooden houses generally include heat insulating walls.
The so-called internal heat insulators widely employed for these purposes each have an athermalized core sandwiched between an outer board and an inner board, wherein the core is usually made of a rock wool or glass wool.
Dew condensation takes place on the inner face of outer board at low outdoor temperatures. Such a condensate will erode the outer board made of plywood or the like and will stain the inner board made for example of a decorative plywood.
The so-called external heat insulators were therefore proposed recently, because no dew tends to condense between the outer and inner boards.
An example of the external heat insulators comprises a heat insulating material such as the so-called `styrofoam` (viz. a trade name of polystyrol foam) bonded to a plywood base plate. This insulator will be attached to an outer face of a skeleton and then lined with mortar. Since the insulating material is disposed outside the outer board, there will arise no problem of dew condensation.
The external heat insulator's of this type also are disadvantageous in that the mortar finish is not sufficiently resistant to fire. These insulators will not be qualified as heat insulators as prescribed in JIS A-1302, unless difficult plaster work is done by a highly skilled plasterer to form a considerably thick outer layer, similar to the usual external walls. This plaster work will entail a longer time, a higher cost and a larger space for the construction work.
It is also proposed to use a light concrete foam called `Autoclaved Light-Weight Concrete` or `ALC` as the external heat insulator.
The `ALC` boards are however not sufficient in heat insulation, also an increased thickness thereof rendering them heavier and causing a longer period and a raised cost of construction. Moreover, `ALC` boards are so hygroscopic that they tend to absorb water which will freeze in the cold season and cold districts. Due to expansion of the ice thus formed in internal pores, these boards are likely to crush or burst.